Combustion Apparatus

ABSTRACT

A combustion apparatus  1  includes an intermediate member  6  constituted by a premixer  2  and a burner port assembly  3  and an air passage member  5 , the intermediate member  6  being interposed between two air passage members  5 . Fuel gas flows into an opening row part  10 . The opening row part  10  has a number of openings  8  arranged linearly, so that the fuel gas introduced into the row part  10  is uniformly discharged through each of the openings  8 . The fuel gas discharged through the openings  8  of the row part  10  bumps into air at mixing spaces  39 . Fuel gas discharged through slots is homogenous and uniform in flow rate. Fuel gas produces a primary flame in a first combustion part  46  to perform a primary combustion. Unburned combustible components are discharged outside through openings of the first combustion part  46  and produce a secondary flame with air supplied through the distal end portion of the air passage member  5.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to combustion apparatuses, and moreparticularly to a combustion apparatus recommended to be used in a waterheater or a bath heater.

2. Description of the Related Art

A combustion apparatus is a main component in a water heater or a bathheater and in widespread use at home as well as at factories.

Recently, environmental destruction resulting from acid rain has becomea grave social issue, and thus, there is a pressing need to reduce atotal amount of emission of NOx (nitrogen oxides).

There is a combustion apparatus employing a combustion system called the“thick and thin fuel combustion” method adapted to be used in a smalldevice such as a water heater and to reduce NOx emissions.

The “thick and thin fuel combustion” method is designed to produce amain flame from a lean gas mixture composed of fuel gas premixed withair of about 1.6 times the amount of the theoretical amount of air andto arrange around the main flame an auxiliary flame produced from a richgas mixture with a small amount of mixed air and a high gasconcentration.

A combustion apparatus based on the thick and thin combustion is knownfor such a configuration as disclosed in the patent documents 1 and 2,for example.

A combustion method with a less amount of NOx emissions also includes acombustion system called the “two-staged combustion” method.

The “two-staged combustion” method is adapted to inject a fuel gas in anoxygen-deficient condition to produce a primary flame by igniting thegas, so as to produce a secondary flame by supplying a secondary air tounburned gas.

The patent document 3 discloses a combustion apparatus employing thetwo-staged combustion method.

Patent Document 1: JP 5-118516A

Patent Document 2: JP 6-126788A

Patent Document 3: JP 52-143524A

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

A combustion apparatus employing the thick and thin fuel combustionmethod generates a less amount of NOx emissions, being well-reputed inthe market, but is disadvantageous in low Turn Down Ratio (T. D. R).Especially, the combustion apparatus employing the thick and thin fuelcombustion method is disadvantageous in difficulty to burn in an areahaving a low heating value.

Specifically, in the thick and thin fuel combustion method, a main flameis produced from a lean gas mixture composed of fuel gas premixed withair of about 1.6 times the amount of the theoretical amount of air, asdescribed above. The gas mixture has a low burning rate because of itsleanness.

The combustion apparatus employing the thick and thin fuel combustionmethod is provided with a fan for facilitating generation of a lean gasmixture, but the fan would become deteriorated due to years of usethereof, resulting in gradually reducing its blowing volume. Clog of afilter of the fan might reduce its air blowing volume. Such a reducedair blowing volume caused by aging is liable to reduce an amount of airin the gas mixture producing a main flame, rendering the amount of mixedair approaching the theoretical amount of air. As a result, a combustionspeed of the main flame is liable to become more rapid due to aging.Therefore, the proximal end of flame is liable to gradually approachburner ports due to aging. Thus, combustion in an area having a lowheating value would render the proximal end of flame approaching toburner ports, resulting in damaging the burner ports. Consequently, acombustion apparatus employing the thick and thin fuel combustion methodis forced to restrict combustion in an area having a low heating valueon an anticipated aging.

In addition, the thick and thin fuel combustion method causes such acomplaint as a narrow range of usable gas. Specifically, fuel gassupplied by a gas maker may be constituted by a single component, but inmany cases, by a plurality of components. That causes differentcombustion speed depending on makers of fuel gas even if their amountsof heat generation (amounts of heat per unit volume) are the same amongthem.

Since the thick and thin fuel combustion method produces a main flame inan air excess condition, fuel gas having a slow combustion speed mightcause blow off, resulting in an unstable combustion.

In contrast, the two-staged combustion method can have a higher TurnDown Ratio than the thick and thin fuel combustion method. Further, awide variety of fuel gas is available. However, the two-stagedcombustion method burns fuel gas in an oxygen-deficient condition,resulting in an unstable combustion. Provably for this reason, we foundnone of practical devices such as water heaters that are offeredcommercially and employ the two-staged combustion method.

In order to put to practical use as a combustion apparatus, it isnecessary to produce such flame as to uniformly spread over a certainarea. This can be achieved by producing a primary flame and a secondaryflame in a balanced manner and uniformly throughout the entire area of acombustion site.

However, it is difficult to produce the primary and the secondary flamesin a balanced manner and to uniformly distribute the flames throughoutthe entire area of the combustion site. For example, the primary flamemight be partly extinguished, resulting in an excessive secondary flameat downstream thereof, or all fuel might burn out at a site to producethe primary air, resulting in extinguishment of the secondary flame atdownstream thereof. Therefore, we found no combustion apparatusemploying the two-staged combustion method, among devices such as waterheaters having put to practical use.

An object of the present invention made in view of the problems anddrawbacks in the art described above is therefore to improve acombustion apparatus performing two-staged combustion and to developsuch a combustion apparatus as producing a primary flame and a secondaryflame in a balanced manner and spreading the flames uniformly throughoutthe entire area of a combustion site.

Means to Solve the Problem

In order to solve the problems and drawbacks described above, an aspectof the present invention provided herein is a combustion apparatus,including at least one premixer adapted to premix therein fuel gas andair and having an opening row part with openings arranged in a row, atleast one air passage member of a wall shape having at least one distalair emission opening at its distal end, and at least one burner portassembly arranged between two of the air passage members or between theair passage member and another wall, having a burner port-upstreampassage formed between the opening row part and the burner port assemblyand a first combustion part formed by a space enclosed by the burnerport assembly and the air passage member, so that the air is supplied tothe air passage member, the burner port-upstream passage, and thepremixer, and so that the fuel gas is supplied to the premixer to bepremixed with the air within the premixer, and whereupon the resultingair-fuel gas mixture is supplied through the openings of the opening rowpart into the burner port-upstream passage to be further mixed with airand to be discharged through the burner port assembly into the firstcombustion part in an oxygen-deficient condition, so as to burn and tofurther burn upon air supply through the distal air emission opening ofthe air passage member.

The present aspect has the premixer, in which fuel gas and air arepremixed. The premixer has the opening row part with the openingsarranged in a row, through which the fuel gas is distributed to theburner port-upstream passage. The fuel gas is mixed with air also in theburner port-upstream passage. Therefore, according to the configurationof the present aspect, the resulting air-fuel gas mixture flowing in theburner port-upstream passage is well mixed and homogenous. Consequently,the homogenized fuel gas is discharged through all areas of walls of theburner port assembly. That produces a primary flame and a secondaryflame in a balanced manner and spreads the flames uniformly throughoutthe entire area of a combustion site.

It is preferable to have a certain space adjacent to the opening rowpart and within the burner port-upstream passage. This space becomes amixing space in which fuel gas and air are mixed. The openings of theopening row part are preferably open toward the mixing space.

Further, it is preferable that the mixing space extends substantiallyover full width of the opening row part.

The mixing space extending in this way promotes homogenization ofpressure.

It is preferable that the openings of the opening row part are open in adirection cross to a flowing direction of the air flowing in the burnerport-upstream passage.

Fuel gas is discharged in a direction cross to the air flow directionthrough the openings of the opening row part, having frequent bumpinginto the air. That promotes mixture of the fuel gas and the air.

A variety of configurations can be considered as the burner portassembly. An employed configuration, for example, may be such that theburner port assembly includes a burner port-forming part and two sidewalls and has an opening between the two side walls and on the siteopposite to the burner port-forming part, wherein the opening row partof the premixer is surrounded by the side walls, and wherein the air issupplied through the opening between the walls.

Further, it is recommended to have such a configuration that the airpassage member has a combustion part-facing air emission opening foremitting air therefrom toward the first combustion part. At this time,it is preferable that the burner port assembly has a plurality of burnerport groups, the combustion part-facing air emission opening beingarranged at a site corresponding to between the burner port groups ofthe burner port assembly.

The first combustion part is a site where the primary flame is produced,whereas the secondary flame is produced outside of the first combustionpart by air supplied through the distal air emission opening. Thecombustion part-facing air emission opening is arranged so as todischarge air from the side toward between the burner port groups of theburner port assembly, so that the air is blown from surroundings of theburner port groups, thereby ensuring stabilizing the primary flame.Further, the air is supplied from under the primary flame, so as toproduce the secondary flame at an early stage and perform a completecombustion of fuel gas adjacent to the primary flame. That allowscompact combustion space, thereby shortening the total length of theprimary and the secondary flames. The proximal end of the secondaryflame is also stabilized.

It is recommended that the air passage member has an inclined surface,on which the combustion part-facing air emission opening is formed.

According to this arrangement, air is jetted in an oblique direction,without obstructing the flow of a main part of the primary flame or theflow of fuel gas.

Further, according to this arrangement, the air is introduced along theflow of the main part of the primary flame or the flow of fuel gas,without accumulating in the vicinity of the wall of the air passagemember.

Specifically, fuel gas flows substantially parallel to the wall withinthe first combustion part. Thus, in the case of introducing air in adirection perpendicular to the first combustion part from the airpassage member, the air bumps into the primary flame or the fuel gas,resulting in possible accumulation. If air accumulates in the vicinityof the wall of the air passage member, the accumulated air may causecombustion of surrounding unburned gas and produce flame in the vicinityof the wall of the air passage member. The wall may be excessivelyheated and glow.

In response, the air jetted in an oblique direction is introduced alongthe flow of the primary flame or the flow of fuel gas, so as to producethe secondary flame at a site distant from the air passage member. Thatavoids glowing of the wall of the air passage member.

Further, it is also recommended that the air passage member has anupstream air emission opening for emitting air and at upstream of a partof the member defining the first combustion part, the air emittedthrough the upstream air emission opening flowing toward a side of theburner port assembly.

According to the above-mentioned arrangement, air discharged through theupstream air emission opening flows toward the side of the burner portassembly, so that oxygen is supplied to the side of the burner portassembly. That produces stable flame at the side of the burner portassembly, holding the proximal end of the primary flame. As aconsequence, the primary flame is stabilized.

Still further, it is also recommended that the burner port assembly hasa central opening and a side opening, so that the fuel gas is dischargedthrough the side opening slower than the fuel gas discharged through thecentral opening, and the air flows in the vicinity of the side openingof the burner port assembly.

This arrangement makes a clear distinction between the burner port forproducing a main part of the primary flame and the burner port forproducing an auxiliary flame.

Specifically, according to the above-mentioned arrangement, the flowrate of fuel gas discharged through the side opening is slower than thatof fuel gas discharged through the central opening, and whereby flameproduced at the side opening is hardly blown off. Further, air issupplied to the vicinity of the side opening, so that fuel gasdischarged through the side opening performs a relatively stablecombustion and holds the proximal end of the primary flame. As aconsequence, the primary flame is stabilized.

The side opening may be constituted in such a manner that the burnerport assembly is constituted by a main body and a decompression walldisposed at a side of the main body, the main body and the decompressionwall defining therebetween a gap that has a side opening, and the mainbody having an opening, through which a part of the fuel gas flowing inthe main body flows into the gap.

According to the above-mentioned arrangement, fuel gas is introducedthrough the opening formed on the main body into the gap formed betweenthe side wall and the decompression wall, but an amount of the fuel gas(more properly, the fuel gas premixed with air) is restricted by theopening, so that the flow rate of the fuel gas discharged through theside opening becomes slower than that of fuel gas discharged throughother sites.

The openings of the opening row part each may be of a slot-like shape.

Further, the opening row part may have an inclined surface, on which theopenings are formed. At this time, the opening row part has preferablyan inner angle at 180 degrees or less.

Fuel gas is discharged in an oblique direction by forming the openingson the inclined surface. That allows the fuel gas more frequent contactwith air flow, promoting mixture of fuel gas and air.

Further it is recommended that the distal end of the air passage memberis of an acute-angled ridge-like shape.

The air emission opening is formed on the distal end of the air passagemember, so as to supply secondary air. According to the above-mentionedarrangement, the distal end of the air passage member is of anacute-angled ridge-like shape, thereby ensuring less air flowing aroundwithin the member. That stabilizes a discharging direction of air.

ADVANTAGEOUS EFFECT OF THE INVENTION

The combustion apparatus of the present invention produces the primaryand the secondary flames in a balanced manner and uniformly distributedthroughout the entire area of the combustion site, being practical.

Further, the combustion apparatus of the present invention achieves aless amount of NOx emissions and a higher Turn Down Ratio. Stillfurther, the combustion apparatus of the present invention is widelyadapted to fuel gas having any combustion speed, so as to be used forall types of gas.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional perspective view conceptually illustrating aconfiguration of a combustion apparatus of the present invention;

FIG. 2 is a perspective view of a combustion apparatus in a practicalembodiment of the present invention;

FIG. 3 is a plan view of the combustion apparatus in FIG. 2 accommodatedin a casing;

FIG. 4 is a sectional view taken along the lines A-A of FIG. 3;

FIG. 5 is a sectional view of the combustion apparatus in FIG. 2;

FIG. 6 is a perspective view showing an internal structure of thecombustion apparatus broken in a stepwise fashion;

FIG. 7 is an exploded perspective view of the combustion apparatus inFIG. 2;

FIG. 8 is an exploded sectional view of the combustion apparatus in FIG.2;

FIG. 9 is a perspective view of a premixer of the combustion apparatusin FIG. 2;

FIG. 10 is a sectional view taken along the lines A-A of FIG. 9;

FIG. 11 is a sectional view taken along the lines B-B of FIG. 9;

FIG. 12 is a perspective view of an air passage member of the combustionapparatus in FIG. 2;

FIG. 13 is an enlarged view of a concaved part of the air passage memberin FIG. 12;

FIG. 14 is a perspective view of a burner port assembly of thecombustion apparatus in FIG. 2;

FIG. 15 is an enlarged front view of a trough for engagement of theburner port assembly in FIG. 14;

FIG. 16 is a side view showing the burner port assembly joined to thepremixer;

FIG. 17 is an enlarged view showing the vicinity of the proximal end ofthe burner port assembly in FIG. 16;

FIG. 18 is an illustration diagram showing a positional relationshipbetween openings of the premixer and ribs of the air passage member;

FIG. 19 is an illustration diagram showing a positional relationshipbetween openings of a premixer and ribs of an air passage member ofanother embodiment;

FIG. 20 is an illustration diagram showing air flow within the airpassage member of the present embodiment;

FIG. 21 is an illustration diagram showing air flow within the airpassage member of another embodiment;

FIG. 22 is an exploded perspective view of a combustion apparatus ofanother embodiment;

FIG. 23 is an exploded perspective view of a combustion apparatus ofstill another embodiment; and

FIG. 24 is a partly enlarged plan view showing a positional relationshipbetween burner port groups of the burner port assembly and combustionpart-facing air emission openings of the air passage member.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Now, an embodiment of the present invention will be described below indetail, making reference to the accompanying drawings. First, an outlineconfiguration and basic functions of the present invention will bedescribed, referring to a schematic view of FIG. 1. An embodiment inFIG. 1 conceptually illustrates the present invention.

In the following descriptions, the vertical positional relationship isbased on a combustion apparatus 1 positioned upright and producing flameat an upper part thereof. Terms “upstream” and “downstream” are based onan air or fuel gas flow. A “width direction” denotes a lateral direction(a direction of an arrow “W” in the figure) with a part having themaximal area of the combustion apparatus facing the front.

The combustion apparatus 1 of the present embodiment is used byaccommodating more than one apparatus in a casing or alone. Thecombustion apparatus 1 includes a premixer 2, a burner port assembly 3,and two air passage members 5. In the combustion apparatus 1, thepremixer 2 and the burner port assembly 3 are engaged with each other toconstitute an intermediate member 6, which is interposed between the twoair passage members 5. However, in the actual use, a plurality of theair passage members 5 and a plurality of the intermediate members 6 arealternately arranged to form a planar shape in an order such as the airpassage member 5, the intermediate member 6, the air passage member 5,the intermediate member 6, the air passage member 5, and so on.

The premixer 2, a component of the combustion apparatus 1, serves topremix fuel gas and air therewithin. The premixer 2 includes a mixingpart 7 having a curved passage and an opening row part 10 havingopenings 8 arranged in a row. The opening row part 10 has a cavity of asubstantially square shape in a cross section extending lengthwise andlinearly.

The air passage member 5 generally has a thin wall shape. The airpassage member 5 is constituted by a first face 11 and a second face 12,each made of a thin plate, in such a manner that the first and thesecond faces 11 and 12 are connected with forming a narrow gaptherebetween, the three sides except the bottom being joined, therebydefining a cavity to be an air passage 13 inside.

Specifically, the first and the second faces 11 and 12 are made byfolding a unitary plate. Its distal end has an acute-angled bent portion14, the bent portion 14 making up a top portion 9, which extends inridge-like lines.

The proximal end of the air passage member 5 is open between plates ofthe first and the second faces 11 and 12, forming an air inlet 15.

In the air passage member 5, openings for emitting air are formed atthree areas. Since the air passage members 5 and the intermediatemembers 6 are alternately arranged to form a planar shape, as describedabove, the same numbers of openings are formed at the same portions ofthe first and the second faces 11 and 12 of the air passage members 5.

The openings for emitting air are formed at the distal end, a positionfacing to a first combustion part 46, and a position facing to theintermediate member 6, roughly describing.

Specifically, the plates of the first and the second faces 11 and 12 ofthe air passage member 5 are arranged in parallel in their most parts,but are angularly folded only at their distal ends, forming inclinedsurfaces 16 and 17 at the first and the second faces, respectively. Theinclined surfaces 16 and 17 each have distal openings 20. Further,distal openings 21 are formed at a tip (ridge line). The distal openings20 and 21 are formed for supplying a secondary air to a secondary flame.

The first and the second surfaces 11 and 12 of the air passage member 5,as shown in FIG. 1, has the air passage 13 formed in such a manner asbeing narrower at its distal end than at its proximal end and havingsteps at positions corresponding to the proximal end of the firstcombustion part 46, which steps also constitute inclined surfaces 22.Combustion part-facing air emission openings 23 are formed at each ofthe steps. The air emission openings 23 are designed to supply thesecondary air therethrough to the primary flame in the first combustionpart 46, so as to bum part of the primary flame to produce the secondaryflame within a part of the first combustion part 46.

Further, air emission openings (upstream air emission openings) 48 areformed at a position facing to the intermediate member 6. The airemission openings (upstream air emission openings) 48 serve to stabilizean auxiliary flame by supplying air therethrough to each side of theburner port assembly 3.

The burner port assembly 3 is mainly constituted by a main body 25 anddecompression walls 26. The main body 25 of the burner port assembly 3is made by bending a piece of metal plate, having a top face 30functioning as burner ports and two side walls 31 and 32 bent at asubstantially 90 degree angle at the both edges of the top face 30.Right and left sides of the burner port assembly 3 are closed with onlyits bottom in the figure opened. The top face 30 of the burner portassembly 3 has an elongated shape with an A-line shape cross section.The top face 30 has slots regularly arranged, which constitute burnerports 33. The burner ports 33 formed at the main body 25 function as“central openings.”

The side walls 31 and 32 each have a protruding part 34 protrudingoutwards (in a thickness direction) at its intermediate portion. Theprotruding part 34 is formed across the full width of the burner portassembly 3.

Open ends of the side walls 31 and 32 are bent at a substantially 90degree angle twice as shown in the figure, each forming outside a trough(or a gutter) 38 for engagement. The troughs 38 have bottom walls 36vertical to and outer walls 37 parallel to the respective side walls 31and 32.

The decompression walls 26 are attached to the main body 25, asdescribed above. The decompression walls 26 are fixed to the respectiveside walls 31 and 32 of the main body 25, forming gaps 29 between therespective side walls 31 and 32 of the main body 25. The gaps 29 eachhave an opening at a top of the figure. The opening functions as a sideopening 27.

Openings 35 are formed at the side walls 31 and 32 and at positionsfacing to the decompression walls 26. The gaps 29 are communicated withan inner space of the main body 25 via the openings 35.

Next, a relationship between components will be described below.

In the present embodiment, as described above, the premixer 2 and theburner port assembly 3 are engaged, thereby constituting theintermediate member 6. More specifically, the opening row part 10 of thepremixer 2 is placed between the side walls 31 and 32 of the burner portassembly 3. In the actual producing process, the premixer 2 is insertedfrom the opening (bottom in the figure) between the side walls 31 and 32of the burner port assembly 3 to join the both members.

The side walls 31 and 32 and the opening row part 10 have partly contactwith each other by their concave and convex shapes not shown, thus beingunified. As described above, the side walls 31 and 32 and the openingrow part 10 have partly contact with each other by their concave andconvex shapes, and in other words, they partly keep away from eachother. The cross section in FIG. 1 shows a cross section at a site wherethe side walls 31 and 32 and the opening row part 10 keep away from eachother.

Sites corresponding to the protruding parts 34 of the side walls 31 and32 are away from the accommodated opening row part 10. The protrudingparts 34 each correspond to a row of openings 8 of the opening row part10. Thus, outsides of the openings 8 of the opening row part 10 keepaway from the side walls 31 and 32, so as to form spaces (mixing spaces)39 wider than the other portions. The spaces 39 extend over full widthcorresponding to all the openings 8.

A relatively large space 47 is formed between the side walls 31 and 32and between the top of the opening row part 10 and the top face 30 ofthe burner port assembly 3. In the present embodiment, the mixing spaces39 and the space 47 downstream of the opening row part 10 form a burnerport-upstream passage 49.

The air passage members 5 are attached to the both sides of theintermediate member 6. Each of the air passage members 5 is joined withthe intermediate member 6 by engaging the air inlet 15 of the proximalend of the member 5 with the trough 38 of the burner port assembly 3.Specifically, the outer wall 37 of the trough 38 is inserted into theair inlet 15 and the tip of the air passage member 5 is inserted intothe trough 38, and whereby the air passage member 5 is brought intocontact with the bottom wall 36 of the trough 38.

The air passage member 5 and the intermediate member 6 (the burner portassembly 3) have partly contact with each other by the concave andconvex shape, and thus the both members are unified. The both membershave partly contact with each other as just described, and in otherwords, keep partly away from each other. The cross section of FIG. 1shows a site where the air passage member 5 and the intermediate member6 (burner port member 3) keep away from each other so as to facilitateunderstanding their functions. However, at an end (the bottom edge inthe figure) upstream of the combustion apparatus 1, a space 40 betweenthe air passage member 5 and the intermediate member 6 are closed by thebottom wall 36 of the trough 38. Thus, the space 40 between the airpassage member 5 and the intermediate member 6 is not directlycommunicated with outside at the proximal end.

The burner port assembly 3 is interposed between the two air passagemembers 5 as described above, the top face 30 of the assembly 3 lyingbelow (in the figure) the top level of the air passage members 5 and, soto say, buried between the air passage members 5. Therefore, a spaceahead of the top face 30 of the assembly 3 is partitioned by walls ofthe two air passage members 5. In the present embodiment, a spaceenclosed by the top face 30 of the assembly 3 and the two air passagemember 5 functions as the first combustion part 46.

Next, a function of the combustion apparatus 1 will be described indetail below.

A number of the combustion apparatus 1 are opposed within a casing notshown, with air being sent by means of a fan 41 from the bottom in thefigure. Fuel gas is introduced into the apparatus 1 through a gas inlet43 of the premixer 2 by means of a nozzle 42.

First, air flow will be described. The air flow is shown by thin linesin FIG. 1.

Air blow generated by the fan 41 is straightened through openings 45 ofa straightening vane 44 so as to be introduced into the combustionapparatus 1 through the proximal end (bottom in the figure) of theapparatus 1.

There are three routes for air introduced into the apparatus 1. Thefirst route passes through inside the air passage member 5, the airflowing through the air inlet 15 formed at the proximal end of the airpassage member 5 into the air passage member 5 and going up to thedistal end through the air passage 13 within the air passage member 5.Most of the air is discharged outside through the distal openings 20 and21.

Part of the air flowing in the air passage member 5 is discharged alsothrough the combustion part-facing air emission openings 23 and the airemission openings (upstream air emission openings) 48.

The air having been discharged through the air emission openings 23 isdischarged in a direction diagonally to the front of an axis line of theapparatus 1 from the inclined surfaces 22 of the steps.

Further, the air having been discharged through the air emissionopenings 48 flows in the space 40 between the air passage member 5 andthe intermediate member 6 to the side of the burner port assembly 3.

The second route passes through inside the intermediate member 6. Theintermediate member 6 is constituted by the opening row part 10 of thepremixer 2 interposed between the side walls 31 and 32 of the burnerport assembly 3. Gaps (openings) exist between the opening row part 10and the burner port assembly 3 and a part of the gaps (openings) is openat the bottom of the intermediate member 6.

Therefore, the air is introduced through the openings 28 into betweenthe premixer 2 and the side walls 31 and 32 of the burner port assembly3.

This air flows through the gaps between the side walls 31 and 32 and theopening row part 10, entering the mixing spaces 39, and then flowinginto the space 47 between the opening row part 10 and the top face 30 ofthe burner port assembly 3. That is, the air described above flows inthe burner port-upstream passage 49. Finally, the air is dischargedthrough the slots, i.e., the burner ports 33, into the first combustionpart 46. Part of the air having entered the space 47 enters the gaps 29between the main body 25 and the side walls 31 and 32 through theopenings 35 formed on the side walls 31 and 32 of the main body 25 andis discharged into the first combustion part 46 through the sideopenings 27.

Next, the third route for air will be described in detail below. Thethird route is a route for the primary air, which is introduced withfuel gas through the gas inlet 43 of the premixer 2. The third route isthe same route as that of fuel gas flow, being illustrated in thefollowing description as that of the fuel gas flow. The fuel gas flow isindicated by arrows in solid line in FIG. 1.

Fuel gas is introduced into the third route with the primary air throughthe gas inlet 43 of the premixer 2 to be mixed with air in a part suchas the mixing part 7, the resulting mixture flowing into the opening rowpart 10. The opening row part 10 has a number of openings 8 arrangedlinearly, so that the fuel gas having been introduced thereinto isevenly discharged through each of the openings 8. The fuel gas havingbeen discharged through the openings 8 of the row part 10 enters themixing spaces 39 formed between the side walls 31 and 32 of the burnerport assembly 3 and the openings 8 of the row part 10 to be mixed withair flowing in the burner port-upstream passage 49 (including the mixingspaces 39).

The air flowing in the burner port-upstream passage 49 (including themixing spaces 39) flows vertically (from bottom to top), whereas thefuel gas having been discharged through the openings 8 of the row part10 flows in a direction perpendicular to the air flow. Thus, the fuelgas hits hard the air also at the mixing spaces 39, and whereby mixingof the fuel gas with the air 5 is facilitated. Further, the mixingspaces 39 each extend throughout in a longitudinal direction of theopening row part 10, thereby smoothing pressure.

After having passed through the mixing spaces 39, the fuel gas flowsinto the space 47, during which the mixing of the fuel gas with the airis enhanced. After that, the fuel gas flows in the same way as the flowin the burner port-upstream passage 49, entering the space 47 betweenthe opening row part 10 and the top face 30 of the burner port assembly3, and being mostly discharged through the slots (the burner ports) 33into the first combustion part 46. Part of the air having entered thespace 47 enters the gaps 29 between the decompression walls 26 and thesidewalls 31 and 32 of the main body 25 through the openings 35 formedon the side walls 31 and 32, being discharged through the side openings27 into the first combustion part 46.

The fuel gas having been discharged through the burner ports 33 is mixedwith air within the premixer 2 and further mixed with air within themixing spaces 39, and thus, being uniformed and being discharged throughthe burner ports 33 at a uniform rate.

However, though the fuel gas discharged through the burner ports 33 ismixed with air, an amount of the air is below a theoretical amount ofair. That is why the fuel gas discharged through the burner ports 33 isin an oxygen-deficient condition, failing in achieving a completecombustion only with this fuel gas.

Ignited, the fuel gas produces the primary flame in the first combustionpart 46, so as to perform a primary combustion. However, the fuel gas isnot completely burned because of insufficient oxygen as described above,resulting in generating a great deal of unburned combustible component.

The unburned combustible component is discharged outside through openingof the first combustion part 46. Herein, air is supplied to outside ofthe first combustion part 46 through the distal end of the air passagemember 5. Therefore, the unburned combustible component performs asecondary combustion upon oxygen supply. In other words, an area outsideof the first combustion part 46 functions as a secondary combustion partand produces the secondary flame.

Further, in the present embodiment, air is supplied to the proximal endof the primary flame, so as to produce an auxiliary flame in theproximal end of the primary flame.

In the present embodiment, fuel gas is discharged not only through theburner ports 33, i.e., the “central openings,” but also through the sideopenings 27. However, the flow rate of fuel gas discharged through theside openings 27 is slower than that of fuel gas discharged through theburner ports 33. Specifically, the fuel gas enters the gaps 29 betweenthe decompression walls 26 and the side walls 31 and 32 of the main bodythrough the openings 35 formed on the side walls 31 and 32, beingdischarged through the side openings 27 into the first combustion part46. That restricts an amount of fuel gas entering the gaps 29, resultingin a small amount of fuel gas discharged through the side openings 27.Conversely, the side openings 27 each have a large opening space. Thus,the fuel gas discharged through the side openings 27 has a low flowrate.

Further, as described above, part of air passing though the air passagemember 5 is discharged through the air emission openings (upstream airemission openings) 48 into the space 40 between the air passage member 5and the intermediate member 6, reaching the side faces of the burnerport assembly 3 through the space 40. Therefore, the side faces of theassembly 5 3 is richer in oxygen than other parts, ensuring that thefuel gas discharged through the side openings 27 performs a relativelystable combustion with reception of air supply.

Coupled with a low flow rate of the fuel gas as described above, astable auxiliary flame is produced in the vicinity of the side openings27. The proximal end of the primary flame is held by small flamesproduced in the vicinity of the side openings 27.

Still further, in the present embodiment, the air having been dischargedthrough the combustion part-facing air emission openings 23 stabilizesthe secondary flame. Specifically, in the present embodiment, theinclined surfaces 22 are located at the first and the second faces 11and 12 of the air passage member 5 and at sites corresponding to theproximal ends of the first combustion part 46. The air emission openings23 are formed on the inclined surfaces 22, thereby supplying airdiagonally to an air flow direction from the proximal end of the firstcombustion part 46. Thus, the supplied air is supplied into the firstcombustion part 46 without obstructing the primary flame or the flow ofunburned gas. As a consequence, part of unburned gas within the firstcombustion part 46 starts combustion and partly produces a secondaryflame, which merges with the external secondary flame, therebystabilizing the secondary flame produced outside.

Yet further, in the present embodiment, the combustion part-facing airemission openings 23 are diagonally open, without obstructing theprimary flame or the flow of unburned gas, as described above.Consequently, the secondary flame is produced at a distance from the airpassage member 5 and does not excessively heat the air passage member 5.

The combustion apparatus of the present embodiment therefore stabilizesboth the primary and the secondary flames, thus being practical.

Now, a more practical configuration example of the present inventionwill be described in referring to the following figures after FIG. 2.The embodiment described below is practically designed for embodying thepresent invention and has the most recommended configuration.

A combustion apparatus shown in the figures following after FIG. 2 hasthe same basic configuration and basic function as those in theabove-mentioned embodiment, but is practically designed to detail. Thesame numerals are assigned to components that carry out the samefunctions as those in the foregoing embodiment, and descriptions of theduplicated functions are simplified.

A plurality of combustion apparatuses 1 shown in FIG. 2 are accommodatedin parallel in a casing 54 as shown in FIGS. 3 and 4. The combustionapparatus 1 of the present embodiment also includes a premixer 2, aburner port assembly 3, and air passage members 5. The premixer 2 andthe burner port assembly 3 are engaged to constitute an intermediatemember 6, which is interposed between the two air passage members 5.

A shape of the premixer 2 is shown in FIGS. 9, 10, and 11. The premixer2 is formed by a unitary sheet steel pressed and molded into an unfoldedform having a concave and convex shape on its surface, which is bent andconnected at its periphery by means of a spot welding. The spot weldingis done at flanges 51 of the periphery.

The premixer 2 after assembly has such a shape that a front plate 52 asshown in FIGS. 8 and 9 is coupled with a rear plate 53 symmetric to thefront plate 52. The premixer 2 has a rounded shape with a flat top part50 and is sealed at its periphery so as to prevent gas from beingleaked.

The premixer 2 forms therein a unitary gas passage between the front andthe rear plates 52 and 53. Specifically, the sheet steel forms a spaceat a portion where the concave and convex shapes of the front and therear plates 52 and 53 correspond to each other, thereby forming the gaspassage by the space.

In the premixer 2 employed in the present embodiment, as shown in FIG.9, the gas passage is roughly divided into upper and lower parts. Morespecifically, the gas passage mainly consists of a mixing passage 19 andan opening row part 10.

Referring to FIG. 9, the mixing passage 19 is formed at the lower partof the premixer 2, from an entrance of the gas passage to the openingrow part 10. Starting with the entrance of the passage, a gas inlet 43is open at the corner of the lower part of the combustion apparatus 1.The gas inlet 43 has therein a squeezed portion 55 where itscross-sectional area is locally squeezed and at downstream thereof adiameter expansion portion 56 where the cross-sectional area isgradually expanded. A uniform cross-section portion 57 having a uniformcross-sectional area continues at further downstream. The passage fromthe gas inlet 43 through the squeezed portion 55 and the diameterexpansion portion 56 to the uniform cross-section portion 57 isstraight.

The end of the uniform cross-section portion 57 is connected to theopening row part 10 with the passage bent at a right angle.

Herein, in the present embodiment, a portion just before the opening rowpart 10 is not squeezed.

Referring to FIG. 9, the opening row part 10 is located at the upperpart of the premixer 2 and extends throughout in a longitudinaldirection. A cross-sectional area of the row part 10, in other words,the space between the front and the rear plates 52 and 53 at the rowpart 10 is wide, as shown in FIGS. 10 and 11.

Referring to FIGS. 10 and 11, the row part 10 has a cross section oftwo-tiered configuration with a small area portion 58 having a slightlysmall cross-sectional area near the top part 50.

Specifically, the row part 10 has such a cross section that the top part50 is flat with upper part vertical walls 81 vertically extending fromits both sides. Bottom edges of the upper part vertical walls 81 eachare connected to inclined walls, extending slightly outward. Further,bottom edges of the inclined walls are contiguous to lower part verticalwalls 82.

The small area portion 58, which is an outer surface of the row part 10,has a number of openings 8 at both of the front and the rear plates 52and 53. The openings 8 are formed linearly in a row at predeterminedintervals.

In the present embodiment, the openings 8 are formed only at the frontand the rear sides of the row part 10, and not at the top part 50.

Next, the air passage member 5 will be described in detail below, inreferring to FIGS. 8, 12, and 20. The air passage member 5 is alsoformed by a unitary sheet steel pressed and molded into an unfolded formhaving a concave and convex shape on its surface, which is bent andconnected at its periphery by means of a spot welding. The air passagemember 5, as shown in FIG. 8, is constituted by a first face plate 11and a second face plate 12 joined at their periphery with a small gap,which forms a cavity to be an air passage 13.

The distal end of the air passage member 5 has an acute-angled bentportion, which constitutes a top portion 9 extending in ridge-likelines.

The air passage member 5, as shown in FIG. 12, has flanges 83 at bothsides adjoining the bent portion, the flanges 83 being secured eachother at the both sides by means of a spot welding.

The proximal end of the air passage member 5 is open between the firstand the second face plates 11 and 12, which form an air inlet 15.

Referring to FIG. 12, the air passage member 5 is of a thin wall shapeand roughly divided into three areas in a height direction in itsupright position.

Specifically, the areas consists of an introduction portion 60 from theproximal end to about one third of the total height, an intermediateportion 61 from the introduction portion 60 to about two thirds thereof,and a first combustion part-forming portion 62 of another one third nearthe distal end.

The air passage member 5 constitutes a passage headed toward the distalend from the air inlet 15, a cross-sectional area of the passagebecoming narrower toward the distal end.

Specifically, the portion from the air inlet 15 to about one third ofthe total height (the introduction portion 60), as shown in FIG. 8, hasa substantially uniform cross-sectional area. In other words, in theintroduction portion 60, the first and the second face plates 11 and 12are parallel without changing intervals therebetween as shown in thecross section in FIG. 8.

The intermediate portion 61 has a roughly tapered shape.

Specifically, as shown in the figures, the intermediate portion 61 isextended in a tapered shape with its lower part being wider andnarrowing as going upward. However, a protruding portion 84 is formedbetween the distal end of the tapered portion and the first combustionpart-forming portion 62. Both sides of outer walls defining theprotruding portion 84 are parallel.

The first combustion part-forming portion 62 has a substantially uniformcross-sectional area (except the top portion 9), but its cross-sectionalarea per unit length is about one third compared with that of theintroduction portion 60. Steps composed of inclined surfaces 22 areformed between the portion 62 and the portion 61.

The air passage member 5 has openings for emitting air at three areas.The areas consist of the distal end portion, a position facing to afirst combustion part 46, and a position facing to the intermediatemember 6, roughly describing.

Specifically, the first and the second face plates 11 and 12 of the airpassage member 5 are angularly folded at their distal ends, forminginclined surfaces 16 and 17 at the first and the second face plates,respectively. The inclined surfaces 16 and 17 each, as shown in FIG. 12,have circular distal openings 20. Circular distal openings 21 are alsoformed at the tip portion (ridge line portion).

Further, in the present embodiment, the top portion 9 and the inclinedsurfaces 16 and 17 have distal openings 63 and 64 of short and longslot-like shapes. The shorter distal openings 63 each extend over entireheights of the inclined surfaces 16 and 17 and the top portion 9. Thelonger distal openings 64 each extend from portions where the first andthe second face plates 11 and 12 are in parallel to the top portion 9.

The longer slots (distal openings) 64 are larger in number than theshorter slots (distal openings) 63; two or three of the longer slots 64being arranged in a row, thereafter the shorter slot 63 being arranged,then two or three of the longer slots 64 being arranged in a row, and soon. Such a sequence of arrangement is made over all area in alongitudinal direction of the air passage member 5.

The above-mentioned circular distal openings 20 and 21 are formedbetween two of the slots (distal openings) 63 or 64.

The distal openings 20 and 21 are, as well as in the foregoingembodiment, formed for supplying a secondary air to a secondary flame.

Further, combustion-part-facing air emission openings 23 are formed onthe inclined surface 22 between the first combustion-part formingportion 62 and the intermediate portion 61. The air emission openings 23are to supply a secondary air to a primary flame taking place in thefirst combustion part 46, so as to burn a part of the primary flame andproduce a secondary flame.

Still further, air emission openings (upstream air emission openings) 48are formed adjacent to the boundary between the introduction portion 60and the intermediate portion 61. The air emission openings (upstream airemission openings) 48 serves to supply air to a side of the burner portassembly, so as to stabilize an auxiliary flame.

The first and the second face plates 11 and 12 of the air passage member5 each have concave and convex shapes at each portion for forming a gapbetween the both plates or between each plate and another member.

Describing successively, near the distal end, a plurality of troughs 70and 71 extending heightwise are formed on walls defining the firstcombustion part-forming portion 62. The troughs 70 and 71 each have aconcave or hollow shape in surface view and extend heightwise inparallel. The trough 70 is shorter than the trough 71. The troughs 70and 71 are formed mainly for strengthening the plates.

In the present embodiment, the troughs 70 and 71 are arranged over fullwidth of the air passage member 5 in such a sequence of arrangement as aplurality of the short troughs 70, thereafter a plurality of the longtroughs 71, then a plurality of the short troughs 70, and so on.

Further, the distance between the long troughs 71 are wider than thatbetween the other troughs.

Concaved parts 72 each as shown in FIGS. 12 and 13 are formed everybetween the long troughs 71 and adjacent to the proximal end of the longtroughs 71. The concaved parts 72 each have also a streamline shape anda concave shape in surface view. More specifically, the concaved parts72 each are formed by a large circle and a small circle with theircenters displaced from each other and a common tangent connecting thecircles, the large circle being located at upstream of the air passageand the small circle being located at downstream of the air passage. Aline connecting the centers of the two circles is in parallel to an airflowing direction. The common tangent connecting two circles have aninclination angle of 30 degrees or less relative to the line connectingthe centers of the circles.

Six ribs 73 are formed, as shown in FIG. 12, on the intermediate portion61 of the air passage member 5. The ribs 73 each are arranged inparallel to an air flowing direction. The ribs 73 each have contact withan outer surface of the intermediate member 6 so as to form a gaptherebetween, as described below, and have a tip (ridge), whose location(distance from the center line of the air passage member 5) isthoroughly at the same level at any site. Specifically, as describedabove, the intermediate portion 61 has a tapered cross section of thepassage, but the height of the ribs 73 (size of protuberances) increasesin an inverse tapered manner as going upward, the location of the tipsbeing at the same level.

A number of troughs 75 are also formed in parallel on the introductionportion 60. The troughs 75 each extend from the proximal end of the airpassage member 5 toward the distal end and have a concave shape insurface view.

A trough 77 extends in a transverse direction (in a directionperpendicular to an air flow) adjacent to the introduction portion 60.

The trough 77 is formed mainly for positioning.

A protuberance 80 of a substantially triangular shape is formed on thecentral portion at each side of the air passage member 5.

Now, the burner port assembly 3 will be described below. Referring toFIGS. 8 and 14, the burner port assembly 3 is constituted by a main body25 with a decompression wall 26 welded at its each side.

The main body 25 of the assembly 3 is also formed by a unitary sheetsteel pressed and molded into an unfolded form having a concave andconvex shape on its surface, which is bent and connected at itsperiphery by means of a spot welding. The main body 25, as shown in FIG.14, has flanges 85 at both sides adjoining a top face 30, being joinedby the flanges 85, and a face opposite to the top face 30 is open.

The main body 25 of the assembly 3, as shown in FIGS. 8 and 14, has thetop face 30 functioning as burner ports and two side walls 31 and 32bent at a substantially 90 degree angle at the both edges of the topface 30. The top face 30 of the assembly 3 has an elongated shape withan A-line shape cross section. The top face 30 is of a roof-like shape,with a ridge portion 86 at the center being the highest and its bothsides being gradual inclined walls 87.

As described above, the burner port assembly 3 is made by bending apiece of metal plate, which is tucked down at the ridge portion 86 ofthe top face 30. Thus, as shown in the figure, the tucked portionprotrudes downward as a vertical wall 88 within a cavity of the assembly3.

The top face 30 of the main body 25 has slot-like openings, whichconstitute burner ports (central openings) 33. Each of the slots (burnerports 33) extends in a width direction of the top face 30. A pluralityof the slot-like openings are formed in parallel over all area in alongitudinal direction of the top face 30. As shown in FIG. 14, aplurality of slot-like openings make up a burner port group 89, aplurality of the burner port groups 89 being arranged at regularintervals on the top face 30.

As to a cross section of the main body 25, as shown in FIG. 8, the mainbody 25 has two squeezed portions 78 and 79. Conversely, there are twoprotruding portions, i.e., a distal protruding portion 90 and anintermediate protruding portion 91, except a proximal end portion.

Specifically, the main body 25 has the distal protruding portion 90including the top face 30 described above and the intermediateprotruding portion 91 formed at the middle portion. The distal squeezedportion 78 is formed between the intermediate protruding portion 91 andthe distal protruding portion 90. The proximal squeezed portion 79 isformed adjacent to the proximal end of the intermediate protrudingportion 91.

Among the protruding portions 90 and 91 and the squeezed portions 78 and79 described above, the distal protruding portion 90 and theintermediate protruding portion 91 are formed over full width of theburner port assembly 3.

Small openings 35 are formed, as shown in FIG. 14, in a row on the sideof the distal protruding portion 90.

The proximal squeezed portion 79 has a plurality of ribs 92, as shown inFIG. 14. The ribs 92 each protrude outside in surface view; in otherwords, form a trough 93 within the cavity, as shown in FIG. 6. The ribs92 each extend in a height direction of the assembly 3 and are arrangedin parallel in a width direction of the assembly 3.

Open ends of the side walls 31 and 32 are, as shown in FIGS. 6, 8, 16,and 17, bent at a substantially 90 degree angle twice, each formingoutside a trough (or a gutter) 38 for engagement. The troughs 38 havebottom walls 36 vertical to and outer walls 37 parallel to therespective side walls 31 and 32.

The outer wall 37 constituting the trough 38 has a front view of asubstantially trapezoidal shape. Specifically, the both sides of theouter wall 37 are inclined as shown in an enlarged view in FIG. 15 in atapered shape. Further, as shown in FIGS. 16 and 17, the side walls 31and 32 within the troughs 38 each have protuberances 95. Theprotuberances 95 are positioned at both ends of the trough 38,respectively; one protuberance 95 for each end.

The decompression walls 26 are fixed to the upper ends of the respectiveside walls 31 and 32 of the main body 25. The decompression walls 26each are, as shown in FIG. 14, an elongated plate, covering the entirearea of the distal protruding portion 90 of the main body 25. Gaps 29are formed between the decompression walls 26 and the respective sidewalls 31 and 32 of the main body 25. The gaps 29 each have an opening ata top of the figure. The opening functions as a side opening 27. Herein,the decompression wall 26 has, as shown in FIG. 8, a small protuberance97 on its inner surface, the protuberance 97 contacting with the mainbody 25 to maintain the distance of the side opening 27.

As described above, the openings 35 (FIG. 14) are formed in a row on thedistal protruding portion 90. The gaps 29 are communicated with an innerspace of the main body 25 via the openings 35.

In the both ends of the main body 25, the side walls 31 and 32 arejoined by a spot welding to constitute flanges 85 and have gaps 98therebetween from the proximal end to the vicinity of the intermediateprotruding portion 91.

Next, relationship between components will be described below, makingreference to FIGS. 5 and 6.

In the present embodiment, the premixer 2 and the burner port assembly 3are engaged to constitute the intermediate member 6, as well.

The burner port assembly 3 (intermediate member 6) is, as describedabove, interposed between the two air passage members 5, the top face 30of the assembly 3 lying below (in the figure) the top level of the airpassage member 5 in the figure and, so to say, buried between the airpassage members 5. Therefore, a space ahead of the top face 30 of theassembly 3 is partitioned by walls of the two air passage members 5. Inthe present embodiment, a space enclosed by the top face 30 of theassembly 3 and the two air passage member 5 functions as the firstcombustion part 46.

The intermediate member 6 is constituted by the burner port assembly 3and the premixer 2 engaged therewith in such a manner as inserting thepremixer 2 with the top part 50 ahead into a cavity of the assembly 3.At this time, the flanges 51 formed at the both sides of the premixer 2are engaged with the gaps 98 formed at the both ends of the assembly 3.Then, the tips of the premixer 2 come into contact with the innermostsof the gaps 98, respectively, and whereby positioning in an insertingdirection is done.

The vertical walls 82 formed at the lower part of the opening row part10 of the premixer 2 come into contact with the inner wall of theproximal squeezed portions 79 of the assembly 3, respectively, andwhereby positioning in a thickness direction is done.

The small area portion 58 of the opening row part 10 of the premixer 2comes to the position of the intermediate protruding portion 91 of theassembly 3.

As for gaps between the opening row part 10 of the premixer 2 and theassembly 3, as described above, the small area portion 58 is situated inthe intermediate protruding portion 91 of the side walls 31 and 32 ofthe assembly 3. Specifically, the intermediate protruding portion 91corresponds to the position of the row parts of the openings 8 of theopening row part 10. Consequently, outer sides of the openings 8 of therow part 10 is away from the side walls 31 and 32, thereby formingspaces (mixing spaces) 39 wider than the other portions. The mixingspaces 39 extend over full width corresponding to all the openings 8.

As described above, the lower part of the row part 10 of the premixer 2has contact with the inner walls of the proximal squeezed portion 79 ofthe assembly 3. Thus, the outer walls of the row part 10 have contactwith the inner walls of the assembly 3 with no space at most sites in awidth direction. However, the proximal squeezed portion 79 has, asdescribed above, a plurality of ribs 92, the inner surfaces of which arethe troughs 93 (FIG. 6). Consequently, the outer walls of the row part10 are kept away from the inner walls of the assembly 3 at the sites ofthe ribs 92. Further, the ribs 92 each extend in a height direction ofthe assembly 3, thereby ensuring that the mixing spaces 39 arecommunicated with the proximal end of the assembly 3.

Herein, as to a positional relationship between the ribs 92 and theopenings 8 formed on the row part 10 of the premixer 2, as shown in FIG.18, the openings 8 are situated above the ribs 92. In other words, theopenings 8 are on extensions of the ribs 92. In the present embodiment,as shown in FIG. 18, the ribs 92 correspond one-to-one with the openings8, but may not correspond, as shown in FIG. 19, in such a manner thatthe openings 8 are more than the ribs 92 or vice versa.

There are gaps between the proximal end of the assembly 3 and thepremixer 2. Thus, the mixing spaces 39 are communicated with outside viathe ribs 92 (troughs 93) and the above-mentioned gaps.

On the other hand, above the mixing spaces 39, there is a relativelylarge space 47 between the side walls 31 and 32 and between the top part50 of the row part 10 and the top face 30 of the assembly 3. In thepresent embodiment, the above-mentioned mixing spaces 39 and the space47 at downstream of the row part 10 constitute a burner port-upstreampassage 49.

Referring to FIGS. 5 and 6, the air passage members 5 are joined withthe both sides of the intermediate member 6. Each of the air passagemembers 5 is secured to the intermediate member 6 by engaging the airinlet 15 at the proximal end of the member 5 with the trough 38 of theburner port assembly 3. Specifically, the outer wall 37 of the trough 38is inserted into the air inlet 15 and the tip of the air passage member5 is inserted into the trough 38, and whereby the air passage member 5is brought into contact with the bottom wall 36 of the trough 38.

Herein, the outer wall 37 of the trough 38 is, as described above, of atrapezoid shape in surface view and has the both sides in a taperedshape, so that the inner wall of the air inlet 15 follows the taperedshape of the outer wall 37 of the trough 38 in joining the air passagemember 5, and whereby positioning in a width direction is done.

When the air passage member 5 fits in a regular place in the burner portassembly 3, as shown in FIG. 17, the protuberances 95 formed in thetrough 38 engage with the outer edges of the trough 77 formed adjacentto the opening of the air passage member 5, with a feeling of clickstop.

Further, when the air passage member 5 fits in the regular place, asshown in FIG. 24, the burner port-facing air emission openings 23 aresituated between the burner port groups 89 of the assembly 3 in a widthdirection.

At the upstream end (the bottom in the figure) of the combustionapparatus 1, the space 40 between the air passage member 5 and theintermediate member 6 is closed by the bottom wall 36 of the trough 38.Thus, the space 40 between the air passage member 5 and the intermediatemember 6 is not directly communicated with outside at the proximal end.

As shown in FIGS. 5 and 6, the distal squeezed portion 78 comes to theside of the upstream air emission openings 48 of the air passage member5. The distal squeezed portion 78 is a concaved portion of the surfaceof the assembly 3, so that there is a gap between the air passage member5 and the assembly 3 adjacent to the upstream air emission openings 48.

Further, the gap is communicated with the first combustion part 46.Specifically, the air passage of the air passage member 5 is taperedtoward the distal end beyond the openings 48, so that the outer wall ofthe air passage member 5 becomes situated to the inward side of the airpassage toward downstream, forming wider space between the member 5 andthe assembly 3. Herein, the outer wall of the air passage member 5 andthe burner port assembly 3 partly contact with each other via the ribs73 formed on the member 5.

Now, a function of the combustion apparatus 1 will be described below.

A number of combustion apparatuses 1 are accommodated in the casing 54as shown in FIG. 3 and air is sent by the fan 41 from the bottom in thefigure as shown in FIG. 4. Further, fuel gas is introduced through thegas inlet 43 of the premixer 2 by means of a nozzle.

Air flows in the substantially same way as the above-mentionedembodiment, that is; air blow generated by the fan 41 is straightenedthrough openings of a straightening vane 44 (FIG. 4) so as to beintroduced into the combustion apparatus 1 through the proximal end(bottom in the figure) of the apparatus 1.

There are three routes for air introduced into the apparatus 1, as wellas in the foregoing embodiment. Specifically, the first route passesthrough the air passage member 5, as shown in FIG. 6, the air blow beingintroduced through the air inlet 15 formed at the proximal end of theair passage member 5 into the air passage member 5 and going up to thedistal end through the air passage 13 within the member 5. Most of theair is discharged outside through the distal openings 20 and 21.

Herein, in the present embodiment, as shown in FIG. 20, the distal endof the air passage member 5 is acute-angled and the distal openings 63and 64 among all the distal openings are slots extending over entireheights of the inclined surfaces 16 and 17 and the top portion 9,thereby preventing air from staying in the distal end portion or causingturbulent flow.

As shown in FIG. 21, for example, in the case that the distal endportion of the air passage member is of a round shape, air havingintroduced through the air inlet 15 bumps into a circular surface of aceiling to flow around the distal end portion along the circularsurface. The air flowing therearound bumps into air flow newly suppliedas indicated by arrows, resulting in disturbing emission of newlysupplied air and distorting an emission direction. In this way, arounded shape of the distal end portion of the air passage member 5generates turbulent flow or air eddy, resulting in an unstable directionof air flow. That causes flicker of the secondary flame. Further,according to the experiments by the inventors, it is noisy.

On the other hand, the present embodiment has the acute-angled distalend portion as shown in FIG. 20, thereby ensuring less portion intowhich supplied air bumps and less air flowing around the distal endportion. Further, the slot-like openings are formed on the inclinedsurfaces, so that most of air bumping into the inclined surfaces isdischarged outside through the slot-like openings. That stabilizes anemission direction of air, causes less flicker of the secondary flame,and reduces the noise. However, in the present invention, a shape of thedistal end of the air passage member is not limited, and may be round asshown in FIG. 21.

In the combustion apparatus 1 of the present embodiment, part of airflowing in the air passage member 5 is discharged also through thecombustion part-facing air emission openings 23 and the air emissionopenings (upstream air emission openings) 48.

The air having been discharged through the combustion part-facing airemission openings 23 is discharged in a direction diagonally to thefront of an axis line of the apparatus 1 from the inclined surfaces 22toward between the burner port groups 89 and 89 of the burner portassembly 3.

The air having been discharged through the openings (upstream airemission openings) 48 flows in the space 40 between the air passagemember 5 and the intermediate member 6, and then reaches the side of theburner port assembly 3. More specifically, the air having beendischarged through the openings 48 is discharged into a gap formed bythe proximal squeezed portion 78 of the burner port assembly 3, and thenflows in the space formed by the tapered wall of the air passage member5 to be discharged to the side of the burner port assembly 3.

The second route passes through inside the intermediate member 6, intowhich air is introduced through the openings 28 into between thepremixer 2 and the side walls 31 and 32 of the burner port assembly 3.

This air flows through the troughs 93 (the reverse side of the ribs 92)formed on the inner surface of the burner port assembly 3, entering themixing spaces 39, and then flowing into the space 47 between the openingrow part 10 and the top face 30 of the burner port assembly 3. That is,the air described above flows in the burner port-upstream passage 49.Finally, the air is discharged through the slots, i.e., the burner ports(central openings) 33, into the first combustion part 46. Part of theair having entered the space 47 enters the gaps 29 between the main body25 and the side walls 31 and 32 through the openings 35 formed on theside walls 31 and 32 of the main body 25 and is discharged into thefirst combustion part 46 through the side openings 27.

Now, the third route for air will be described in detail. The thirdroute is a route for the primary air, which is introduced with fuel gasthrough the gas inlet 43 of the premixer 2. The third route is the sameroute as that of fuel gas flow, being illustrated in the followingdescription as that of the fuel gas flow. The fuel gas flow is indicatedby arrows in solid line.

Fuel gas is introduced into the third route with the primary air throughthe gas inlet 43 of the premixer 2 to be mixed with air in a part suchas the mixing part 7, the resulting mixture flowing into the opening rowpart 10. Herein, in the present embodiment, there is no squeezed portionbetween the uniform cross-section portion 57 and the opening row part10. Thus, the fuel gas enters the opening row part 10 without variationin flow rate in particular.

The fuel gas having entered the row part 10 is uniformly dischargedthrough each opening 8. Specifically, the row part 10 is not too smallinside, thereby dissipating fine eddy generated in a part such as anindirect passage in the premixer 2. Further, as described above, thereis no squeezed portion just before the row part 10, so that the fuel gasintroduced into the row part 10 has small variation in flow rate overthe cross section of the passage. Therefore, the row part 10 has smallvariation in pressure inside, so that the fuel gas is uniformlydischarged through each opening 8. Opening diameters of the openings 8may be narrowed down so as to equalize jetted gas volume.

The fuel gas having been discharged through the openings 8 of the rowpart 10 enters the mixing spaces 39 constituted by the intermediateprotruding portion 91 of the burner port assembly 3, so as to be mixedwith air flowing in the burner port-upstream passage 49 (including themixing spaces 39).

The air flowing in the mixing spaces 39 flows from bottom to top in thefigure and is straightened.

Specifically, the air flowing into the mixing spaces 39, which isintroduced thereinto through the openings 28 between the premixer 2 andthe side walls 31 and 32 of the burner port assembly 3, passes throughthe troughs 93 (the reverse side of the ribs 92) formed on the innersurface of the burner port assembly 3, thus being laminar airflow.

More specifically, in the present embodiment, most portion of theproximal squeezed portion 79 of the burner port assembly 3 has contactwith the outer walls of the premixer 2, but the proximal squeezedportion 79 has a number of troughs 93 formed on its inner surface, thushaving gaps at sites of the troughs 93. Each trough 93 is communicatedwith the mixing spaces 39. Therefore, air having introduced through theopenings 28 between the premixer 2 and the side walls 31 and 32 passesthrough a number of troughs 93, then reaching the mixing spaces 39. Thetroughs 93 are elongated passages arranged in parallel at regularintervals, so that the introduced air is straightened by flowing in aplurality of troughs 93.

The air flowing in the burner port-upstream passage 49 (including themixing spaces 39) flows in a height direction of the apparatus 1,whereas the fuel gas having been discharged through the openings 8 ofthe row part 10 flows into the mixing spaces 39 in a directionperpendicular to the air flow. Thus, the fuel gas having been dischargedthrough the openings 8 of the row part 10 bumps into the air also at themixing spaces 39, so as to be promoted to be mixed with the air.

Additionally, in the present embodiment, the openings 8 of the row part10 are on extensions of the troughs 93 (the reverse side of the ribs92), respectively, so that the air having passed through the troughs 93bumps into the fuel gas having been discharged through the openings 8more certainly.

Further, the mixing spaces 39 extend over full width of the row part 10,thereby smoothing its pressure.

The fuel gas, which passes through the mixing spaces 39, flows upward,and flows into a space formed by the distal protruding portion 90, ispromoted to be mixed with the air during flowing there. Then, most ofthe fuel gas is discharged into the first combustion part 46 through theslots, i.e., the burner ports 33.

The fuel gas having been discharged through the slots is homogenous anduniform in flow rate when being discharged through the slots because thegas is mixed with the air within the premixer 2 and further within themixing spaces 39.

Part of the air having entered the space 47 enters the gaps 29 betweenthe main body 25 and the side walls 31 and 32 through the openings 35formed on the side walls of the main body 25, then being dischargedthrough the side openings 27 into the first combustion part 46.

Being ignited, fuel gas produces the primary flame in the firstcombustion part 46 to perform the primary combustion. Unburnedcombustible components are discharged outside through the openings ofthe first combustion part 46 to perform the secondary combustion withair supplied through the distal end portion of the air passage member 5.

Further, in the present embodiment, air is supplied into the proximalend of the primary flame to produce an auxiliary flame at the proximalend of the primary flame.

In short, in the present embodiment, part of fuel gas is dischargedthrough the side openings 27 into the first combustion part 46. However,the flow rate of the fuel gas discharged through the side openings 27 isslower than that of the fuel gas discharged through the slots.Specifically, the fuel gas enters the gaps 29 between the main body 25and the side walls 31 and 32 through the openings 35 formed on the sidewalls of the main body 25, then being discharged through the sideopenings 27 into the first combustion part 46. Therefore, the fuel gasentering the gaps 29 is restricted in volume, and whereby gas volumedischarged through the side openings 27 is small. However, the sideopenings 27 each have a large opening space, so that the fuel gasdischarged through the side openings 27 flows slowly.

Further, as described above, part of the air passing through the airpassage member 5 is supplied to the fuel gas discharged through the sideopenings 27, thereby ensuring a complete combustion.

Specifically, the air having been discharged through the air emissionopenings (upstream air emission openings) 48 flows through the gapsformed by the side walls of the air passage member 5 and the distalsqueezed portion 78 of the burner port assembly 3 along the gaps formedby the tapered walls of the air passage member 5, then reaching thesides of the burner port assembly 3.

A stable auxiliary flame is produced adjacent to the side openings 27,coupled with a low flow rate of fuel gas as described above. Thus, theproximal end of the primary flame is held by small flames producedadjacent to the side openings 27.

Also in the present embodiment, air is diagonally supplied through thecombustion part-facing air emission openings 23 formed on the inclinedsurfaces 22, thereby starting combustion of part of unburned gas in thefirst combustion part 46 and producing partly a secondary flame. Thissecondary flame becomes continuous with the secondary flame outside.

Further, in the present embodiment, air is discharged to between theburner port groups 89 of the burner port assembly 3, so that the air issufficiently supplied to the vicinity of the burner port groups 89,thereby stabilizing the primary flame certainly.

Also in the present embodiment, the air having been supplied through thecombustion part-facing air emission openings 23 does not obstruct theprimary flame or a flow of unburned gas, thereby producing the secondaryflame at a point distant from the air passage member 5 so as not to heatthe member 5 excessively.

Consequently, the combustion apparatus of the present embodimentstabilizes the first and the second flames, being practical.

The above-mentioned embodiment illustrates the premixer having openingsfor discharging fuel gas at its side by an example. This configurationdischarges fuel gas in a direction perpendicular to an air flow, therebyhaving frequent bumping of fuel gas and air, which promotes mixturethereof.

For exerting the similar effect, such a configuration as diagonallydischarging fuel gas can be considered. As shown in FIG. 22, forexample, inclined surfaces 66 and 67 of a roof-like shape are formed onthe top of a premixer 2, with slot-like openings 68. In the presentembodiment, fuel gas is discharged diagonally in front through theslot-like openings 68. As a consequence, the fuel gas bumps into air, soas to be promoted to be mixed with the air. Further, the presentembodiment hardly causes eddy of fuel gas or air, thereby stabilizingfuel gas concentration.

A combustion apparatus shown in FIG. 23 has slot-like openings 69 formedon the top of a premixer.

It is recommended to discharge fuel gas in a direction cross to an airflow, but the present invention does not except such a configuration asdischarging fuel gas along an air flow as shown in FIG. 23.

In the embodiments shown in the figures following after FIG. 2, eachmember has a number of concave and convex shapes on its surface. Theconcave and convex shapes each exert not only a function of constitutingpassages but also a function of improving rigidity of each plate. Theconcave and convex shape not constituting the passages only exerts thefunction of improving rigidity of each plate.

In each embodiment described above, gaps between metallic platesconstitute a unitary passage. Specifically, a concave portion is formedon one or both plates, thereby forming a gap between the one and theother plates. Herein, it is one of design variations to form a concavedportion or the like on either plate in forming a passage, and thepresent invention is not limited to the above-mentioned embodiments. Inthe above-mentioned embodiments, for example, the second route includesa passage passing between the inner surface of the burner port assembly3 and the outer peripheral surface of the premixer 2 so as to secure thepassage by forming the troughs 93 on the inner surface of the burnerport assembly 3. However, by contraries, a passage may be constituted byforming a concaved portion or the like on the premixer 2.

1. A combustion apparatus, comprising: at least one premixer adapted topremix therein fuel gas and air and having an opening row part withopenings arranged in a row; at least one air passage member of a wallshape having at least one distal air emission opening at its distal end;and at least one burner port assembly arranged between two of the airpassage members or between the air passage member and another wall,having a burner port-upstream passage formed between the opening rowpart and the burner port assembly and a first combustion part formed bya space enclosed by the burner port assembly and the air passage member,so that the air is supplied to the air passage member, the burnerport-upstream passage, and the premixer, and so that the fuel gas issupplied to the premixer to be premixed with the air within thepremixer, and whereupon the resulting air-fuel gas mixture is suppliedthrough the openings of the opening row part into the burnerport-upstream passage to be further mixed with air and to be dischargedthrough the burner port assembly into the first combustion part in anoxygen-deficient condition, so as to burn and to further burn upon airsupply through the distal air emission opening of the air passagemember.
 2. The combustion apparatus as defined in claim 1, having amixing space adjacent to the opening row part within the burnerport-upstream passage, the openings of the opening row part being opentoward the mixing space.
 3. The combustion apparatus as defined in claim1, wherein the mixing space extends substantially over full width of theopening row part.
 4. The combustion apparatus as defined in claim 1,wherein the air flows in the burner port-upstream passage in a flowingdirection and the openings of the opening row part are open in adirection cross to the flowing direction.
 5. The combustion apparatus asdefined in claim 1, wherein the burner port assembly comprises a burnerport-forming part and two side walls and has an opening between the twoside walls and on the site opposite to the burner port-forming part,wherein the opening row part of the premixer is surrounded by the sidewalls, and wherein the air is supplied through the opening between thewalls.
 6. The combustion apparatus as defined in claim 1, wherein theair passage member has a combustion part-facing air emission opening foremitting air therefrom toward the first combustion part.
 7. Thecombustion apparatus as defined in claim 6, wherein the air passagemember has an inclined surface, on which the combustion part-facing airemission opening is formed.
 8. The combustion apparatus as defined inclaim 6, wherein the burner port assembly has a plurality of burner portgroups, the combustion part-facing air emission opening being arrangedat a site corresponding to between the burner port groups of the burnerport assembly.
 9. The combustion apparatus as defined in claim 1,wherein the air passage member has an upstream air emission opening foremitting air and at upstream of a part of the member defining the firstcombustion part, the air emitted through the upstream air emissionopening flowing toward a side of the burner port assembly.
 10. Thecombustion apparatus as defined in claim 1, wherein the burner portassembly has a central opening and a side opening, so that the fuel gasis discharged through the side opening slower than the fuel gasdischarged through the central opening, and the air flows in thevicinity of the side opening of the burner port assembly.
 11. Thecombustion apparatus as defined in claim 1, wherein the burner portassembly is constituted by a main body and a decompression wall disposedat a side of the main body, the main body and the decompression walldefining therebetween a gap that has a side opening, and the main bodyhaving an opening, through which a part of the fuel gas flowing in themain body flows into the gap.
 12. The combustion apparatus as defined inclaim 1, the openings of the opening row part each being of a slot-likeshape.
 13. The combustion apparatus as defined in claim 1, the openingrow part having an inclined surface, on which the openings are formed.14. The combustion apparatus as defined in claim 1, the opening row parthaving an inner angle at 180 degrees or less.
 15. The combustionapparatus as defined in claim 1, the distal end of the air passagemember being of an acute-angled ridge-like shape.